Wheelchairs have been used for a long time to assist people, who are less able, to get around. Typically, the wheelchairs include a frame onto which are mounted, larger rear wheels. Two front wheels usually swivel. A handle is provided at the back to assist in pushing the wheelchair and foot rests are provided in the front for the person sitting in the wheelchair to rest their feet on. A seat and a back rest also are attached to the frame between the wheels and form the balance of the chair.
Some wheelchair occupants are so disadvantaged that they are not capable of any voluntary motion. In such cases, the wheelchairs may be provided with their own power source, such as an electric battery or the like to move the wheelchair. However, many wheelchair occupants are able to propel themselves, in their wheelchairs by hand or foot movements.
Because of the special needs of wheelchair occupants, much attention has been focused to the design of seat cushions to be used to provide the maximum comfort to the wheelchair occupants. For example, often such persons are unable to move easily, to for example, shift their weight. Constant pressure on one point can lead to the loss of circulation and the formation of sores, lesions and the like. Therefore, careful attention has been directed to the development of wheelchair seat cushions. Such seat cushions include typically a foam cushion element surrounded by a cover. The foam cushion element may be sculpted, and even formed from foams of different types, in order to provide maximum comfort.
For example, in U.S. Pat. No. 4,522,447 to Snyder, there is provided a foam seat which has a particular pattern of higher and lower density foam. Referring to FIG. 3, a horse-shoe shaped outer denser foam portion surrounds a second horse-shoe shaped inner less dense foam portion which is more easily compressed. A further denser foam area is provided in the middle of the second horse-shoe. In this manner, the cushion yields most under the regions of highest stress, namely, underneath the hip joints and thigh bones of a person sitting in the middle of the seat cushion. However, this foam arrangement is awkward to make, because it requires separate molding parameters for each of the two foam densities, and it does not solve all of the discomfort problems of wheelchair occupants.
When seated in a wheelchair, the foot rests are typically adjusted to support the part of the weight of the feet and the legs of the occupant, with the balance of the weight being supported under the thighs on the seat cushion. By raising the foot rests, more or less support is required under the thighs on the seat cushion. Ideally, the weight of the occupant should be spread evenly along the seat cushion, to avoid the formation of pressure points which could eventually lead to sores forming. Thus, the foot rests are typically made adjustable, and raised or lowered as needed to fully support the thighs of the occupant on the seat.
Many wheelchair occupants, while suffering from various infirmities, are still able to use and control one or both legs. Even if the legs are not sufficiently strong to be walked upon, there may be enough motor control and strength to propel the wheelchair occupant over short distances by a method known as foot propelling. In this method, the occupant of the wheelchair reaches down with their foot, and strikes the ground somewhat in advance of the wheelchair, and drags the wheelchair forward past their heel. Ideally, foot rests should be adjusted no lower than 2" from the ground, in order to clear uneven ground and other obstructions. For wheelchair users who use foot rests always and do not foot propel, the foot rest height is adjusted so that the front portion of the cushion bears some of the weight of the thigh. This provides for weight distribution over as great an area as possible in order to reduce sifting pressures at the rear of the cushion. For wheelchair users who foot propel, the distance from the top of the cushion to the ground must be lower in order to allow the user to reach the ground with an adequate heel strike for foot propulsion. Most foot propellers use foot rests occasionally. In these situations, foot rest adjustment is higher than what is ideal for weight distribution in order to provide adequate ground clearance.